A brake is an important safety device for a bicycle. The brake uses friction force to achieve the effect of speed reduction. In the brake system, by Pascal principle, brake oil serves to transfer the brake force from the brake lever to a hydraulic pressure caliper to push the piston and the brake pads so as to compress the brake disk to have the effect of braking. The hydraulic pressure brake system has the following advantages: 1. The function of the brake is not so affected by weather, environment, or temperature, however the V brake is deeply affected by rain, earth, or temperature; 2. The brake pad has a longer lifetime; 3. Only a small hand force for braking is necessary. In moving along a downward path, user will feel easy; 4. The wheel rim will not wear; 5. The tire will not be damaged by heat generated by the braking force. Thus the hydraulic pressure brake system is widely used in the bicycles. However it still has the problem that a greater braking force is provided so that it is possible to over brake such that the rider can be thrown over the front wheel or the wheels are locked such that the rider losses control, potentially leading to serious injury. Additional due to heat generated during prolonged braking, i.e. holding the bike at constant speed during a long hill descent, the oil tends to expand leading brake drag issues once the brake lever has been released. In the worst case this heat can vaporize the oil leading to a total loss of braking.
Referring to U.S. Pat. No. 6,435,318, “a two-stage bicycle disk brake assembly with an anti-lock device” is disclosed, in that a bicycle disk brake assembly is provided, which includes a pressure-reducing cylinder attached to a caliper body and formed with an inner chamber and outer chamber. Upon application of an external pressure to a hydraulic fluid, which is filled within a fluid reservoir in the caliper body, the fluid flows from the reservoir to the outer chamber. When the fluid pressure in the outer chamber reaches a first value, an inner check valve is operated so as to permit flow of the fluid from the outer chamber to the inner chamber. Thereafter, when the fluid pressure in the inner chamber reaches a second value and when the external pressure is released, a resilient member biases the fluid in the inner chamber to activate an outer check valve, thereby permitting flow of the fluid from the inner chamber to the outer chamber and subsequently to the reservoir. The pressure reduction cylinder indeed offers an improvement over prior art, but has a couple of drawbacks: 1. Dead point where the rider wants more power but only displaces the inner relief piston. 2. The hydraulic pressure for opening the check valve is un-adjustable and can not match the requirement of various environments or riders preference. 3. It doesn't address the problem of heat dissipation. 4. Also due to the relative large size of the piston the initial brake forces are still high. 5. The max braking force is limited somewhat to the size/mass of the system as it is governed by bore size of the piston, i.e. if you want more braking power the size of the piston will need to increase and thus so will the mass/size of the system.